1. Field of the Invention
The present invention relates to a magnetic detection device for detecting the moving direction of a tooth-shaped magnetic moving body.
2. Description of the Related Art
FIG. 18 is a magnetic-circuit configuration diagram for a conventional magnetic detection device utilizing a magnetic detection element.
FIG. 18(a) is a perspective view; FIG. 18(b) is an elevation view. FIG. 19 is an electric circuit diagram for a conventional magnetic detection device; FIG. 20 is a set of waveforms at respective points in the electric circuit diagram in FIG. 19; FIG. 20 also includes a set of diagrams and a table for explaining the waveforms. The foregoing constituent elements are disclosed in U.S. Pat. No. 6,630,821. The magnetic detection device includes a rectangular-parallelepiped magnet 1 for generating a biasing magnetic field and an IC chip 2 that is provided on the magnet 1 and in which three magnetoresistance elements as magnetic detection elements (magnetoelectric conversion elements) are integrated. The arrow in the vicinity of the magnet 1 indicates the direction in which the magnet 1 is magnetized. First, second, and third magnetoresistance elements (referred to as MR elements) 21a, 21b and 22 included in the IC chip 2 are made to be close to and to face a gear-shaped magnetic rotating body (tooth-shaped magnetic moving body) 4, and in the rotation direction of the tooth-shaped magnetic rotating body, the first, third, and second, magnetoresistance elements 21a, 22, and 21b are arranged in that order. Reference numeral 5 denotes the rotation axis of the gear-shaped magnetic rotating body 4; an arrow 3 for the gear-shaped magnetic rotating body 4 indicates the rotation direction of the gear-shaped magnetic rotating body 4. The first and second MR elements 21a and 21b configure a bridge circuit 23; the third MR element 22 and resistor 6 configure a bridge circuit 30.
The rotation of the gear-shaped magnetic rotating body 4 causes the recesses and the protrusions of the gear-shaped magnetic rotating body 4 to alternately approach to the first, second, and third MR elements 21a, 21b, and 22 of the magnetic detection device 1.
Accordingly, the magnetic field that is applied by the magnet 1 to the first, second, and third MR elements 21a, 21b, and 22 is changed. The change in the magnetic field results in changes in the resistance values of the first, second, and third MR elements 21a, 21b, and 22; thus, as changes in respective voltages across the MR elements, the outputs of two bridge circuit systems can be obtained.
The first MR element 21a in the bridge circuit 23 is preferably connected to a constant-voltage and constant-current power source Vcc; the second MR element 21b is earthed; the connection point 7 between the first MR element 21a and the second MR element 21b is connected to the inversion input terminal of a first comparison circuit 29. One terminal of the resistor 8/9 is connected to the power source Vcc; the other terminal is earthed; the connection point 10 between the resistor 8 and the resistor 9 is connected, as a reference voltage, to the non-inversion input terminal of a first comparison circuit 29.
The third MR element 22 of the bridge circuit 30 is preferably connected to a constant-voltage and constant-current power source Vcc; the resistor 6 is earthed; the connection point 11 between the third MR element 22 and the resistor 6 is connected to the inversion input terminal of a second comparison circuit 36. One terminal of the resistor 12/13 is connected to the power source Vcc and the other terminal thereof is earthed; the connection point 14 between the resistor 12 and the resistor 13 is connected, as a reference voltage, to the non-inversion input terminal of the second comparison circuit 36.
In addition, the first MR element 21a and the second MR element 21b configure a first magnetoelectric conversion element; the third MR element 22 and the resistor 6 configure a second magnetoelectric conversion element. In general, as a magnetic detection element, a magnetoresistance element (an MR element) is utilized. An MR element is an element whose resistance value changes depending on the angle between the magnetization direction and the current direction. The resistance value of the MR element becomes minimal when the current direction and the magnetization direction perpendicularly intersect each other and becomes maximal when the angle between the magnetization direction and the current direction is zero degrees, i.e., when the current direction and the magnetization direction coincide with each other or they are entirely opposite to each other.
The respective outputs of the two bridge circuits described above are converted by the corresponding first and second comparison circuits (first and second magnetoelectric conversion output circuits) 29 and 36 into rectangular waves; one output signal e (of the first comparison circuit 29) is connected to the base of an open-collector output transistor 371 and the D terminal of a D-flip-flop circuit (D-FF) 38; the other output signal f (of the second comparison circuit 36) is connected to the CL terminal of the D-FF 38. The output terminal of the D-FF 38 is connected by way of a resistor 391 to the base of a output transistor 401 whose collector is connected to the power-source terminal Vcc; the emitter of the output transistor 401 is connected to the emitter of the output transistor 371 and earthed by way of a resistor 411. In addition, the D-FF 38 is well known; when the CL input thereof is “L (low-level)”, the output maintains the previous state, regardless of the level of the D terminal; in the case where, when the CL input is a rising edge trigger of “H (high level)”, the D terminal is “H”, the output is rendered “H”; in the case where the D terminal is “L”, the output is rendered “L”.
The output signal h of the output transistor 371 is conveyed to a computer unit 42, connected, in the computer unit 42, to the power-source terminal Vcc, by way of a resistor 15, and further connected to the respective inversion input terminals of third and fourth comparison circuits 44 and 45. One terminal of a resistor 16/17 is connected to the power source Vcc; the other terminal is earthed; the connection point 18 between the resistors 16 and 17 is connected, as a comparison level 1 (reference voltage), to the non-inversion input terminal of the third comparison circuit 44. Similarly, one terminal of a resistor 19/20 is connected to the power source Vcc; the other terminal is earthed; the connection point 24 between the resistors 19 and 20 is connected, as a comparison level 2 (reference voltage), to the non-inversion input terminal of the fourth comparison circuit 45. The comparison level 1 and the comparison level 2 for the foregoing third and fourth comparison circuits 44 and 45, respectively, are different from each other and set in such a way that the comparison level 1 is larger than the comparison level 2; therefore, the output signals of the third and fourth comparison circuits 44 and 45 are different from each other.
Next, the operation will be explained. FIG. 20 is a set of waveforms c to j at the points c to j in the electric circuit diagram in FIG. 19; FIG. 20(a) represents the waveforms in the case where the gear-shaped magnetic rotating body 4 rotates forward; FIG. 20(b) represents the waveforms in the case where the gear-shaped magnetic rotating body 4 rotates backward. In the case of the forward rotation (a), the gear-shaped magnetic rotating body 4 approaches the MR element 21a, the MR element 22, and the MR element 21b in that order, thereby reducing the resistance values of the MR elements; therefore, the output (a rectangular wave signal) e, of the first comparison circuit 29, derived from the signal c in the bridge circuit 23 for the MR element 21a is advanced in phase (occurrence timing) than the output (a rectangular wave signal) f, of the second comparison circuit 36, derived from the signal d in the bridge circuit 30 for the MR element 22.
Accordingly, in the case where the D-FF 38, which is a rising-edge trigger type, is utilized, the output g of the D-FF 38 is always high-level “H (a first signal)”. The output transistor 401 connected to the output of the D-FF 38 becomes “ON”, thereby supplying a current to the resistor 411 connected between the emitter and the ground of the output transistor 371. When the output transistor 371 is “OFF”, the level of the output h is a high level that is decided by the voltage at the power-source terminal Vcc in the computer unit 42, regardless of whether the gear-shaped magnetic rotating body 4 rotates forward or backward; When the output transistor 371 is “ON”, the level of the output h becomes a low level 1 that is decided by the multiplication product of the sum of a current supplied by the output transistor 371 and a current supplied by the output transistor 401 connected to the output of the D-FF 38 and the resistant value of the resistor 411 connected between the emitter of the output transistor 371 and the ground.
In contrast, in the case of the backward rotation (b), the gear-shaped magnetic rotating body 4 approaches the MR element 21b, the MR element 22, and the MR element 21a in that order, thereby reducing the resistance values of the MR elements; therefore, the output f, of the second comparison circuit 36, derived from the signal d in the bridge circuit 30 for the MR element 22 is advanced in phase (occurrence timing) than the output e, of the first comparison circuit 29, derived from the signal c in the bridge circuit 23 for the MR element 21a. Accordingly, the output g of the D-FF 38 is always low-level “L (a second signal)”, whereby the output transistor 401 connected to the output of the D-FF 38 becomes “OFF”; therefore, no current can be supplied through the output transistor 401 to the resistor 411 connected between the emitter of the output transistor 371 and the ground. Accordingly, when the output transistor 371 is “ON”, the level of the output h becomes a low level 2 that is decided by the multiplication product of a current supplied by the output transistor 371 and the resistance value of the resistor 411 connected between the emitter of the output transistor 371 and the ground. In this case, the output h may take three values; the magnitude relationship among the values is in such a way that the high level>the low level 1>the low level 2. In addition, the MR element 21b is a magnetoresistance element; however, the bridge circuit 23 can be realized even when the MR element 21b is replaced by a normal resistor.
As a result, the output g of the D-FF 38 becomes high-level “H” (the first signal) in the case of the forward rotation and becomes low-level “L” (the second level) in the case of the backward rotation. Accordingly, it is made possible to detect the rotation direction, based on the value of the output g of the D-FF 38. In addition, in the case of the forward rotation, the output h of the output transistor 371 becomes a pulse signal having two values, i.e., the high level and the low level 1; in the case of the backward rotation, the output h becomes a pulse signal having two values, i.e., the high level and the low level 2; therefore, it is made possible to detect the rotation direction, based on the value of the low level 1 or 2. Additionally, the rotation position and the rotation speed of the gear-shaped magnetic rotating body 4 can be detected based on the pulse having two values.
Furthermore, the output h of the output transistor 371 is applied to the computer unit 42, the comparison level 1 for the third comparison circuit 44 in the computer unit 42 is set to a level between the high level and the low level 1, and the comparison level 2 for the fourth comparison circuit 45 is set to a level between the low level 1 and the low level 2, so that the rotation direction can be detected. That is to say, the case where no signal appears at the output terminal j of the fourth comparison circuit 45 corresponds to the case where the gear-shaped magnetic rotating body 4 rotates forward; the case where a specific signal appears at the output terminal j corresponds to the case where the gear-shaped magnetic rotating body 4 rotates backward. Additionally, at the output terminal i of the third comparison circuit 44, a specific signal appears in either case of the forward or the backward rotation.
Additionally, as can be seen from the waveform charts in FIG. 20, because the signal c (pulse), in the bridge circuit 23 for the MR element 21a, corresponding to the tooth position of the gear-shaped magnetic rotating body 4 is in synchronization with the pulse at the output h of the output transistor 371, regardless of the rotation direction, the facing condition of the gear-shaped magnetic rotating body 4 (whether the protrusion is facing or the recess is facing the MR element 21a) can be discriminated, based on the pulse at the output h; therefore, the magnetic detection device is useful in a control system that requires such a function. In addition, the conventional magnetic detection device disclosed in U.S. Pat. No. 6,630,821 discriminates the moving direction of the tooth-shaped magnetic moving body, by, as described above, utilizing the rising edge of a single rectangular wave signal; therefore, the timing of detecting the moving direction of the tooth-shaped magnetic moving body is delayed.